A bandwidth squeeze is upon us. As more mobile telephony carriers vie for space in a limited RF spectrum, the need to use bandwidth efficiently has never been more pressing. Adding greater urgency to the need to maximize efficiency within a given bandwidth is the growth of data traffic over mobile networks. Thus, the search is on for eliminating wasted bandwidth and system inefficiencies.
One method of communicating voice and data traffic wirelessly is known as code division multiple access or CDMA. In a CDMA system, multiple channels are shared over a distinct RF carrier. Typical CDMA wireless systems utilize unique codes to identify individual channels that occupy the same radio frequency (RF) carrier. During the initial call set-up, a code is assigned to carry the traffic (typically 20 ms frames made of voice bits and/or data bits) from the base station to the mobile station. The transfer rate for a voice calls on a typical code channel is approximately 9.6–14.4 kbps. For non-voice traffic, higher data rates can be achieved through the use of multiple code channels, i.e. several code channels can be used in parallel to increase the data rate. In this way, multiple channels can deliver 20 ms. frames of data to the mobile concurrently yielding a higher overall data rate. Necessary data rates may change on the fly during the course of a conversation or data transfer, and, thus, it would be efficient to be able to dynamically allocate codes or bandwidth on the fly. In current systems, however, the assignment of a code, or codes, for each mobile station is done during call set-up or through a change of service order during an existing call.
In addition to the fact that the existing method for assigning each code, or codes, does not allow for quickly changing the number of codes allocated to each user, existing systems generally assign a single code channel to a single user. Thus, they do not permit multiple users to share a code channel in the midst of a 20 ms. frame. As an example, consider a voice call on a standard CDMA system. A vocoder takes the analog stream of voice data, for example, and converts the analog stream into a digital data stream of bits. The bits that come from the vocoder are arranged into 20 ms. frames and are sent from a base station to a mobile station typically using a single code on the CDMA carrier signal. In this case, if part of the 20 ms frame is received with errors, there is no way to resend the information and the entire frame is discarded. In addition, by limiting the granularity of the system to code channels in 20 ms. frame allotments, bandwidth is often wasted that is unused within a frame.
Existing CDMA systems are unable to rapidly respond to changes in the offered traffic load, and time is wasted during call set-up or during a change of service order. As wireless systems continue to emphasize data traffic, the potential waste in existing CDMA systems could be even larger due to the rapidly changing load requirements of packet data.
The present invention is directed to overcoming one or more of the above shortcomings with existing CDMA systems.